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Vegetarian French Onion Soup

Baking the onions in the oven, plus deeply savory mushroom broth, gives vegetarian French onion soup a full-flavored twist.

Vegetarian French Onion Soup |

Along with chili and maybe bolognese, French onion soup ranks right up there with kitchen aromas that cut through the dark chill of winter. It’s a Sunday sort of soup that likes a long cook to produce that sweet caramelized onion goodness.

Why vegetarian? I’m not a huge fan of beef or the beef broth that marks classic French onion soup, and I discovered a few years ago that this soup is just as fabulous when you substitute beef broth for … mushrooms! Fabulous flavor and you get the health kick from the mushrooms.

My city has a weird little quirk, where I have never been able to find prepared mushroom broth — neither boxed nor concentrate. It’s just nowhere to be found around here, although surely it must exist somewhere in the world.

No matter. It’s super easy to make a quick homemade mushroom broth using dried mushrooms (and my vegetarian French onion soup recipe tells you how).

Speaking of broths, this year, I’ve become a fan of soup stock concentrates, either powdered or paste. Homemade is always better, but in this house, we go through so much soup that I would have to have a pot of stock simmering just about every day to keep up with demand. I turned to powdered concentrate after reading an interesting review from Cook’s Illustrated (it’s behind a paywall, or I’d link to it), and thought I’d give it a try. I found the reduced sodium versions to be lighter in flavor than boxed stocks, complementing rather than overwhelming the other ingredients in the soup. And, it’s much cheaper than the boxed stocks and is always on hand.

Vegetarian French Onion Soup |

I just had to throw in this photo today. It’s garden planning time, and the gardener in me can’t help but encourage cooks everywhere to plant a little herb garden. Got a brown thumb? No problem. Herbs will convince you that it’s not so brown after all.

Especially if you plant something as hardy and forgiving as thyme. Thyme is an evergreen (like pine trees), and survives all but the worst of winters (and survives those, too, if you cover the plant during the subzero stretches). As an evergreen, the leaves — what we cook with — remain green and lush and usable all year ’round. And, in the spring, the low-growing shrubs flower in a mass of beautiful little blooms that honey bees absolutely adore.

On the day I made this soup, I picked this bundle from my garden to dry and stash in my kitchen spice rack.

Vegetarian French Onion Soup |

Back to the vegetarian French onion soup: you’ll note in the recipe that the onions are cooked in the oven, not on the stove. This is a little technique I borrowed from America’s Test Kitchen, and it produces nearly foolproof caramelized onions. I don’t know whether it’s my stove or me or what, but onions seem to move from lusciously browned to burnt and bitter in a blink of an eye … and six times out of 10, that blink occurs when my back is turned. Baking the onions for a longish spell in the oven works wonderfully, as it gently roasts them to caramelized perfection while producing that delicious fond — bits stuck to the bottom of the pan — that adds extra flavor to the soup.

I hope you caught last Friday’s post about making sourdough starter. Now, I know baking homemade bread isn’t everyone’s cup of tea, but I wanted to show you what fun little bread baking projects you can create with sourdough starter. The adorable bread bowls in these photos are sourdough rye bowls — so tasty and easy to whip up in the stand mixer.

Stay tuned for the recipe later this week!

Karen xo

Vegetarian French Onion Soup |
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Vegetarian French Onion Soup

Prep Time15 mins
Cook Time2 hrs 30 mins
Total Time2 hrs 45 mins
Servings: 4 servings
Author: Karen Gibson


  • 1 ounce dried mushrooms I recommend a mix of porcinis and shiitakes
  • 2 tablespoons neutral medium-heat oil (like grapeseed oil)
  • 7-8 medium yellow onions about 5-6 pounds, thinly sliced into half or quarter moons
  • 1/3 cup dry sherry
  • 2 cups vegetable broth
  • 3 sprigs fresh thyme
  • 1 bay leaf
  • salt and freshly ground black pepper
  • 4 ounces shaved Gruyere cheese
  • Croutons optional if not using bread bowls


  • Preheat oven to 375 deg F. Position rack in the center of the oven (you might have to remove the second rack to accommodate a pot with a lid). Meanwhile, heat oil in a 4 to 5 quart dutch oven (on the stove) on medium heat until shimmering. Add the onions along with a big pinch of salt, and stir well to coat with the oil. Cover and simmer for about 15 minutes, until the onions are soft and translucent.
  • When the oven finishes preheating, give the onions one final stir and spread them evenly on the bottom of the pan. Set the lid askew on the pot, and place in the oven. The onions will need to cook for about 1 1/2 to 2 hours. Check after 45 minutes, giving everything a good stir, resetting the lid again askew. Begin checking the onions about every 10 minutes at the 1:20 hour mark – you don’t want the onions to burn, but if they’re deeply golden brown with some burnt bits stuck to the bottom, they’re ready.
  • While the onions cook in the oven, soak the dried mushrooms in 2 cups of very hot (near boiling) water for 20 minutes. When the mushrooms are nice and soft, strain (and reserve) the liquid through a coffee filter. This is your mushroom broth.
  • Optional: for extra mushroom flavor and to give a nice body to the soup, blend the softened mushrooms with the mushroom broth, and set aside.
  • When the onions are ready, remove the pot from the oven, and immediately place on stove over medium heat. Add 1/4 cup water and begin deglazing the the pan, loosening any baked on bits from the bottom. Pour in the sherry and thoroughly deglaze the pan. Simmer until most of the sherry is evaporated (about 5 minutes). Add the vegetable and mushroom broths, plus the thyme and bay leaf. Reduce heat to medium-low, cover, and simmer for about a half hour. Remove the thyme sprigs and bay leaf.
  • To serve, preheat your oven broiler to low, positioning the rack so that there's plenty of room between the heating element and the rack. Ladle the soup into bowls, arrange the croutons on the surface (if using), and layer the Gruyere over the top. Place the bowls on a baking sheet, and broil until the cheese is melted, just a few minutes (if using bread bowls, take care not to scorch the bread - don't walk away from the oven!).
Nutritional information, if shown, is provided as a courtesy only, and is not to be taken as medical information or advice. The nutritional values of your preparation of this recipe are impacted by several factors, including, but not limited to, the ingredient brands you use, any substitutions or measurement changes you make, and measuring accuracy.

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Recipe Rating

Thalia @ butter and brioche

Monday 9th of February 2015

I am obsessed with your photography and presentation of this french onion soup. Just so beautiful and evocative - I definitely am craving a bowl now!

Julie @ Texan New Yorker

Monday 9th of February 2015

Mushrooms!! Yes, I can totally see that working wonders here as a sub for the beef broth. I love having this in the arsenal, it seems like French Onion Soup is one of those classic dishes that you think of when you're going to be hosting a vegetarian, but then have to go, no, no I can't - beef broth, dang it! No more! :)